This invention related to arc plasma spray fabricated ferrite toroids and more particularly to a novel method for producing an elongated drive wire hole through the toroid during the fabrication process.
Arc plasma spray techniques, hereinafter referred to as APS, for fabricating low cost, high performance, non-reciprocal, millimeter wave ferrite toroid phase shifters are well known in the art. By this technique, a ferrite powder, lithium ferrite powder for example, is deposited around a dielectric core or insert to produce the millimeter frequency ferrite toroid phasor. The APS process produces a bonded ferrite dielectric interface which enhances the performance characteristics of the phase shifter. The tolerance of the center of the ferrite toroid is exactly the dimension of the dielectric insert or core, while the outer dimension of the ferrite toroid is readily machined to within 0.001 inches. After machining, the APS fabricated ferrite toroid is annealed to reduce microwave losses and coercive forces. Heretofore, prior to the application of the ferrite powder, the dielectric core was sliced in half and each dielectric half was provided with identically positioned slots. The two halves were then placed together so that the opposing slots formed a longitudinal hole through which an appropriate drive wire was inserted. A ferrite powder can be arc plasma sprayed around the dielectric core without filling the hole so that the drive wire may be inserted through the hole after the formed ferrite has been machined and processed for proper operation at the desired frequency. However, it has been found that one disadvantage of using two dielectric halves is that the interface there between is a source for cracks in the ferrite phasor. Also, it is possible for the dielectric halves to slip prior to spraying, thereby producing improperly aligned interface walls which may deleteriously affect the performance characteristics of the ferrite. Another disadvantage in using two dielectric core halves is that during the fabrication or machining process, the two core halves may bow outwardly thereby forming an air gap which will also deleteriously affect the phasor performance. Moreover, the cost of a dielectric core using two halves is almost twice that of a solid dielectric core since twice the machining is required. The most significant disadvantage of utilizing the dielectric halves technique for forming drive wire holes is that APS formed ferrite toroid phasors can not be fabricated for frequencies higher than 16 GHz since, at these frequencies, the dielectric core is too thin, usually less than 0.02 inches, to work with halves. As the frequency of operation increases, the dielectric becomes thinner and therefore more difficult to work with.